Field of the Invention
The present invention relates to a sheet stacking device that stores sheets with an image formed by an image forming device such as a copier directly on a stacking tray without performing post-processing, or stacks and stores, on the stacking tray, such sheets that have been formed into sheet bundles through post-processing such as binding processing.
Description of the Related Art
A sheet stacking device of the above type receives sheets discharged from an image forming device, guides them to a sheet discharge path in the device, and stores them in a state where they are stacked on a stacking tray disposed on a downstream side of the sheet discharge path. Alternatively, the sheets are subject to post-processing such as binding processing, and then stacked on the stacking tray.
The stacking tray that stores sheets in a stacked state is moved up and down in accordance with an amount of stacked sheets. Therefore, the sheet stacking device includes a sheet surface detection sensor for detecting a height of a top sheet of the sheets stacked on the stacking tray and an elevation means for raising and lowering the stacking tray based on a detection result of the sheet surface detection sensor.
The above sheet stacking device needs to detect a position of a top surface of the sheets stacked on the sheet stacking tray by using a sensor lever not only during sheet stacking operation but also when the sheet stacking device is turned on, in order to stack and store the sheets or bundles of sheets on the stacking tray in an accurately aligned state (for example, see Patent Document 1).
As an example of detecting a position of a top surface of sheets stacked on the sheet stacking tray, there has been known a technique of providing an optical level sensor and adjusting a height of the sheet stacking tray to be within an appropriate range based on detection results of the level sensor and a sensor flag (for example, see Patent Document 2).
The level sensor in Patent Document 2 detects a height of a surface of sheets stacked on a stacking tray by swinging and emerging above the sheet stacking surface.